Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.63	7.416%	$90.9062	$90.91	$90.90	$90.90
Purchase #2	$223.52	13.106%	$252.8145	$252.81	$252.80	$252.80
Purchase #3	$178.31	3.632%	$184.7862	$184.79	$184.80	$184.80
Purchase #4	$51.61	5.402%	$54.398	$54.40	$54.40	$54.40
Purchase #5	$69.84	5.241%	$73.5003	$73.50	$73.50	$73.50
Purchase #6	$153.98	3.535%	$159.4232	$159.42	$159.40	$159.40
Purchase #7	$176.48	4.863%	$185.0622	$185.06	$185.05	$185.10
7 purchase totals =	$938.37		$1,000.8906	$1,000.89	$1,000.85	$1,000.90